High efficiency, high performance computer tape drives are driven by tape transport systems which utilize air bearings designed to suspend the tape on a cushion of air as the tape passes over the read/write head(s). By significantly reducing tape friction and the associated noise and vibration, much higher data density and transfer rates are possible. The absolute performance and reliability of the system depend upon a supply of air to the bearings which is clean, and has minimal flow pulsations. The pulsation amplitude and frequency of the air supply must be within a predetermined narrow range determined by the natural frequencies of the computer tape drive system so as not to excite a resonant condition in the tape drive system. The air source must also be extremely quiet, high in efficiency and generate little heat.
Although conventional double-acting diaphragm air pumps are known to provide a source of clean air with minimal flow pulsations, they are inherently noisy and, if continuously operated, have a short lifetime. In the conventional double-acting diaphragm pump, the motor drives an eccentric which, in turn, drives one or more yoke members for converting rotational motion into rectilinear motion. The yoke member(s) flex the diaphragm assemblies which operate the valves. The drive assembly between the eccentric and each diaphragm is conventionally designed to operate through a separate yoke drive or by using a common yoke arranged in an oval slot, known to those skilled in the art as a Scotch yoke. In reference to the former, unless the yokes are extremely long in length, the use of individual yokes will impart a highly non-linear motion to the diaphragm assembly. This is detrimental to long life and not very practical, particularly for the subject application in which the pump has to be compact and as small in size as possible. A Scotch yoke arrangement is inherently noisy because the drive bearing must alternately impact opposite sides of the oval slot.
The non-diaphragm pump is unsatisfactory because it requires a lubricant which can contaminate the supply of air, is generally noisy and of much lower efficiency compared to the diaphragm pump.